Thermoplastic polymers useful for injection molding and extrusion to form molded articles and films often are deficient in one or more properties. Efforts to modify the properties of a polymer that is otherwise suitable, for example, by blending it with another polymer usually produce an opaque or cloudy blend which is not acceptable when the molded article or film must be clear and transparent. For example, U.S. Pat. No. 4,141,927 to White et al. discloses blends of polyetherimides and of polyesters based primarily on terephthalic acid and isophthalic acid. The patent discloses blends which formed multiple phase solid state solutions in the composition range from about 25 to 90 weight percent polyester. Such compositions are understood to be opaque and cloudy. Blends of polyarylates with polyetherimide are disclosed in the U.S. Pat. No. 4,250,279 to Robeson et al., and U.S. Pat. No. 4,908,419 to Holub et al. Three components blends of polyetherimide, polyester and a third polymer are also disclosed in U.S. Pat. No. 4,687,819 to Quinn et al. and U.S. Pat. No. 4,908,418 to Holub. None of these patents suggests a polymer composition having the combination of desired flexural properties, clarity and transparency.
There is a continuing need for thermoplastic polymer compositions that have high flexural moduli, high flexural strength and high heat deflection temperatures and that can be injection molded or extruded to form articles of excellent clarity and transparency.